The present invention relates to a new and improved fluid responsive indicator and particularly to a liquid level warning device which may easily be installed on existing equipment such as machine tools having a lubricating oil reservoir.
Direct reading liquid level indicators such as sight gauges are limited in their application. Highly viscous liquids will coat the window of a conventional sight gauge making the level difficult or impossible to read. High pressure liquids may cause the window to blow out, crack or leak. Temperature and pressure changes cause aging of the window sealant resulting in leakage.
Bypass type liquid level indicators, while isolated from the liquid being monitored, require two fluid connections to the container for the liquid. Bypass indicator response time increases with the viscosity of the liquid. Also, for liquids subject to re-crystallization upon cooling, the bypass unit and lines must be heated to the same temperature as the process container. Bypass indicator connections require numerous fittings, all of which are subject to leakage. Floats utilized in bypass indicators, the floats carrying a magnet, are subject to friction along the stand pipe walls. Such friction effects operation and results in wear to the stand pipe. The spacing between the bypass indicator and the float magnet to which it is responsive results in the need to employ supplemental magnets to completely rotate the flag magnets of the indicator. Since the flag magnets occupy discrete intervals in the indicating column, the indicated level only approximates the actual level. The actual level can be anywhere between successive flag magnet trip points. Samples of prior art bypass-type liquid level indicators may be seen from U.S. Pat. Nos. 530,592, 1,040,127, 2,233,572 and 4,512,190.
Additional examples of indicators which employ the field provided by a moving magnet to actuate visually observable signalling devices may be seen from U.S. Pat. Nos. 1,081,843, 1,253,324, 1,617,287, 1,723,172, 2,920,484, 3,024,659, 3,420,103, 3,505,869, 3,964,312, and 4,194,397.